Many technical applications can benefit from rechargeable electrical energy storage. Most rechargeable electrical energy storage systems are based on rechargeable batteries. Rechargeable batteries store and release electrical energy through electrochemical reactions. Rechargeable batteries are used for automobile starters, portable consumer devices, light vehicles (such as motorized wheelchairs, golf carts, electric bicycles, and electric forklifts), tools, and uninterruptible power supplies. Emerging applications in hybrid internal combustion-battery and electric vehicles are driving the technology to reduce cost, weight, and size, and increase lifetime. Grid energy storage applications use rechargeable batteries for load-leveling, storing electric energy at times of low demand for use during peak periods, and for renewable energy uses, such as storing power generated from photovoltaic arrays during the day to be used at night. Load-leveling reduces the maximum power which a plant must be able to generate, reducing capital cost and the need for peaking power plants. Small rechargeable batteries are used to power portable electronic devices, power tools, appliances, and so on. Heavy-duty batteries are used to power electric vehicles, ranging from scooters to locomotives and ships. Rechargeable batteries are also used in distributed electricity generation and stand-alone power systems. Such applications often use rechargeable batteries in conjunction with a battery management system (BMS) that monitors battery parameters such as voltage, current, temperature, state of charge, and state of discharge and protects against operating the battery outside its safe operating area. Rechargeable batteries have drawbacks due to relatively large weight per unit energy stored, a tendency to self-discharge, susceptibility to damage if too deeply discharged, susceptibility to catastrophic failure if charged too deeply, limited power availability per unit weight, limited power availability per unit energy, relatively long charging times, and degradation of storage capacity as the number of charge-discharge cycles increases.
Alternatives to batteries for rechargeable energy storage include capacitor-based systems. Capacitors store energy in the form of an electrostatic field between a pair of electrodes separated by a dielectric layer. When a voltage is applied between two electrodes, an electric field is present in the dielectric layer. Unlike batteries, capacitors can be charged relatively quickly, can be deeply discharged without suffering damage, and can undergo a large number of charge discharge cycles without damage. Capacitors are also lower in weight than comparable batteries. Despite improvements in capacitor technology, including the development of ultracapacitors and supercapacitors, rechargeable batteries store more energy per unit volume. One drawback of capacitors compared to batteries is that the terminal voltage drops rapidly during discharge. By contrast, battery systems tend to have a terminal voltage that does not decline rapidly until nearly exhausted. Also, because the energy stored on a capacitor increases with the square of the voltage for linear dielectrics and at a power greater-than or equal to 2 for meta-dielectrics, capacitors for energy storage applications typically operate at much higher voltages than batteries. Furthermore, energy is lost if constant current mode is not used during charge and discharge. These characteristics complicate the design of power electronics for use with meta-capacitors and differentiate the meta-capacitor management system from battery management systems that are presently in use
It is within this context that aspects of the present disclosure arise.